The present invention relates to a method and a detecting device for determining a fungal infection of a plant.
It is known that the health of plants can be assessed by detecting and analyzing the chlorophyll content in plant leaves. If the health of a plant is affected the chlorophyll content in the leaves of this plant is reduced. This reduction can be detected by the light that is reflected by the leaves of the plant.
U.S. Pat. No. 6,366,681 B1 describes a method for generating a chlorophyll-based health map for a geographic area. According to this method, a satellite, and airplane or another elevated device passes over a farmer's field and an imaging device records a multi-spectral digital image. Based on this multi-spectral digital image the chlorophyll content of the leaves of the farmer's field is analyzed, and a chlorophyll-based health map is created.
U.S. Pat. No. 6,855,933 B2 describes an optical spectral reflectance sensor and controller. The sensor obtains the reflectance properties of a plant. By observing the reflected light at particular wavelengths and the intensity of the light source at the same wavelengths, the expected crop yield with a particular level of available nitrogen and the maximum crop yield, if an ideal amount of nitrogen fertilizer is added, are calculated.
U.S. Pat. No. 7,715,013 B2 describes an optical system for plant characterization. In particular, a stressor of a plant is determined. In the method reflected solar energy from a plant surface is collected, the collected solar energy is formed into a multi-band image, and this image is analyzed.
U.S. Pat. No. 7,408,145 B2 describes a light sensing instrument with a modulated polychromatic source. By this apparatus the plant status is assessed using biophysical and biochemical properties of the plant remotely sensed. A single polychromatic emitter provides coincident light beams. A detector array detects portions of this polychromatic light beam reflected by a surface area and provides a signal indicative of whether the detected light was reflected by a plant or by some non-plant object, such as soil. Based on this signal, the plant may be sprayed by a herbicide, or a fertilizer is applied.
U.S. Pat. No. 7,910,876 B2 describes a plant sensor that includes a light source section having first and second light emitters configured to irradiate first and second measuring light toward an object to be measured and a light receiver configured to receive reflected light from the object to be measured. Based on output light-receiving signals information regarding a growing condition of the object to be measured is obtained.
Further, U.S. Pat. No. 8,179,533 B2 describes a sensing system and method for discriminating plant matter. The sensing system comprises a light source having three or more distinct wavelengths for illuminating a plurality of distinct areas in a field of view, a sensor for measuring the reflectance of distinct areas at each of the distinct wavelengths, and an identifier for identifying at least one object in the field of view from the measured reflectance at each of the wavelengths. This system may be used to detect pests, such as insects.
The method and systems described above have the disadvantage that a disease of a plant such as a fungal infection may only be detected if the disease has affected the plants so that the reflection properties of the plant have changed.
Finally, US 2010/0184117 A1 describes a method for determining the content of a non-fluorescent chromophorous first compound, in a biological tissue including a fluorescent chromophorous second compound. The method includes the emission of a first reference optical radiation, and a second measurement optical radiation, each chosen so as to induce a fluorescence radiation of the second compound, each of the first and second radiations being partially absorbed by the first compound. The fluorescence radiations induced by each of the first and second radiations are measured and the content of the first compound in the tissue is determined from the measurement. Moreover, US 2011/0186752 A1 describes a method for determining the ratio of the contents of chlorophyll and of a chromophorous compound that is non-fluorescent in the band of chlorophyll fluorescence in a plant tissue, without determining the contents.